Abstract
The Humboldt-09 cruise covered a narrow meridional band along the Chilean continental slope (44–23º S). Here we use physical and biochemical data from a long meridional section (4000 km) and three short zonal sections (100 km) to describe the distribution of the different water masses found in this region. Six water masses were identified: Subantarctic Water (SAAW), Summer Subantarctic Water (SSAW), Subtropical Water (STW), Equatorial Subsurface Water (ESSW), Antarctic Intermediate Water (AAIW), and Pacific Deep Water (PDW). For the first time, a novel set of source water mass properties (or water types) is introduced for SSAW, and nutrient and dissolved oxygen water types are proposed for all the water masses. Optimum multiparameter (OMP) analysis was used through an iterative process to obtain a sound definition of the water types that minimizes the residuals of the method. Both the classic OMP and the quasi-extended OMP models reproduced the data rather well. Finally, the spatial distribution of the different water masses was calculated with the quasi-extended OMP, which is not influenced by the respiration of organic matter. The distribution of the different water masses is presented over the meridional and zonal transects and in property-property diagrams. A smooth meridional transition from subantarctic to tropical and equatorial water masses is observed in this area. This transition takes place in surface, central, and intermediate waters over distances of the order of 1000 km. The meridional transition contrasts with the abrupt zonal changes found in the cross-slope direction, which are of comparable magnitude but over distances of the order of 100 km. Both AAIW and SAAW (fresh and well oxygenated) partially mix with the hypoxic ESSW and, therefore, play an important role in the ventilation of the southern part of the oxygen minimum zone.
Highlights
The current system off central and northern Chile is quite complex, with the alternation of equatorward and poleward currents that bring different water masses over a zonal band of a few hundred kilometers
In these tropical and temperate regions, near the slope, we encounter a poleward current system. This poleward flow is commonly split into an undercurrent adjacent to the slope, the Poleward Undercurrent (PU), and a further offshore surface current, the Peru-Chile Counter Current (PCCC) (Strub et al 1998), it is likely that the latter is the surface and offshore manifestation of the former
For the first time we describe an additional water mass off central and southern Chile that results from SAAW modified by relatively fresh water coming from intensified spring runoff and summer melting from the fjord region between 40o and 45o S, here named Summer Subantarctic Water (SSAW)
Summary
The current system off central and northern Chile is quite complex, with the alternation of equatorward and poleward currents that bring different water masses over a zonal band of a few hundred kilometers (fig. 1). The HC feeds into the South Equatorial Current (SEC) and its cold tongue can be appreciated as far as 4o S (Penven et al 2005). In these tropical and temperate regions, near the slope, we encounter a poleward current system. Near the shelf we find an equatorward Peru-Chile Coastal Current (PCC), which is wind-driven by the southerly winds and originates off northern and central Chile either from the WWD or from a reversal of the poleward currents (Halpin et al 2004). In the subpolar region the single dominant poleward current, the Cape Horn Current (CHC), experiences substantial buoyancy gain due to high precipitation while being driven by poleward downwelling winds (Halpin et al 2004)
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